linux-kernel - Re: [PATCH v5 0/5] MAP_DIRECT and block-map-atomic files

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Date:   Wed, 16 Aug 2017 16:42:08 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jan Kara <jack@...e.cz>, Arnd Bergmann <arnd@...db.de>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Linux API <linux-api@...r.kernel.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5 0/5] MAP_DIRECT and block-map-atomic files

On Wed, Aug 16, 2017 at 12:44 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> Changes since v4 [1]:
> * Drop the new vma ->fs_flags field, it can be replaced by just checking
>   ->vm_ops locally in the filesystem. This approach also allows
>   non-MAP_DIRECT vmas to be vma_merge() capable since vmas with
>   vm_ops->close() disable vma merging. (Jan)
>
> * Drop the new ->fmmap() operation, instead convert all ->mmap()
>   implementations tree-wide to take an extra 'map_flags' parameter.
>   (Jan)
>
> * Drop the cute (MAP_SHARED|MAP_PRIVATE) hack/mechanism to add new
>   validated flags mmap(2) and instead just define a new mmap syscall
>   variant (sys_mmap_pgoff_strict). (Andy)
>
> * Fix the fact that MAP_PRIVATE|MAP_DIRECT would silently fallback to
>   MAP_SHARED (addressed by the new syscall). (Kirill)
>
> * Require CAP_LINUX_IMMUTABLE for MAP_DIRECT to close any unforeseen
>   denial of service for unmanaged + unprivileged MAP_DIRECT usage.
>   (Kirill)
>
> * Switch MAP_DIRECT fault failures to SIGBUS (Kirill)
>
> * Add an fcntl mechanism to allow an unprivileged process to use
>   MAP_DIRECT on an fd setup by a privileged process.
>
> * Rework the MAP_DIRECT description to allow for future hardware where
>   it may not be required to software-pin the file offset to physical
>   address relationship.
>
> Given the tree-wide touches in this revision the patchset is starting to
> feel more like -mm material than strictly xfs.
>
> [1]: https://lkml.org/lkml/2017/8/15/39

For easier testing / evaluation of these patches I went ahead and
rebased them to v4.13-rc5, fixed up 0-day reports from the ->mmap()
conversion, and published a for-4.14/map-direct branch here:

    https://git.kernel.org/pub/scm/linux/kernel/git/djbw/nvdimm.git/log/?h=for-4.14/map-direct